Introducing manganese complexes as redox mediators for dye-sensitized solar cells

Abstract

The abundance and low toxicity of manganese have led us to explore the application of manganese complexes as redox mediators for dye sensitized solar cells (DSCs), a promising solar energy conversion technology which mimics some of the key processes in photosynthesis during its operation. In this paper, we report the development of a DSC electrolyte based on the tris(acetylacetonato)manganese(III)/(IV), [Mn(acac)₃]^0/1+, redox couple. PEDOT-coated FTO glass was used as a counter electrode instead of the conventionally used platinum. The influence of a number of device parameters on the DSC performance was studied, including the concentration of the reduced and oxidized mediator species, the concentration of specific additives (4-tert-butylpyridine, lithium tetrafluoroborate, and chenodeoxycholic acid) and the thickness of the TiO₂ working electrode. These studies were carried out with a new donor–π–acceptor sensitizer K4. Maximum energy conversion efficiencies of 3.8% at simulated one Sun irradiation (AM 1.5 G; 1000 W m⁻²) with an open circuit voltage (V_OC) of 765 mV, a short-circuit current (J_SC) of 7.8 mA cm⁻² and a fill factor (FF) of 0.72 were obtained. Application of the commercially available MK2 and N719 sensitizers resulted in an energy conversion efficiency of 4.4% with a V_OC of 733 mV and a J_SC of 8.6 mA cm⁻² for MK2 and a V_OC of 771 mV and a J_SC of 7.9 mA cm⁻² for N719. Both dyes exhibit higher incident photon to current conversion efficiencies (IPCEs) than K4.